Switching devices, such as contactors, are manufactured having a rated control supply-voltage. Paragraph 7.2.1.2 of the VDE 0660-100 or IEC/EN/D1N EN 60947-1 standards indicates limit values for operating switching devices having a mechanical drive.
For example, it is specified that a contactor must be switched on at between 85% and 110% of its rated control supply-voltage. This applies to both DC and AC voltages. If a range is given for the rated control supply-voltage, 85% refers to the lower voltage value, and 110% refers to the upper voltage value.
An electronically controlled contactor must be released at between 75% and 20% of the rated control supply-voltage for AC voltage or at between 75% and 10% of the rated control supply-voltage for DC voltage, i.e. said contactor may be released at 75%, but must have been released at 20% and 10%, respectively. If a rated control supply-voltage range is given for operating the contactor, 20% or 10% refers to the upper voltage value, and 75% refers to the lower voltage value.
The rated control supply-voltage range (also referred to herein as the rated voltage range for short) must not be too large as mutually exclusive voltage ranges could otherwise overlap, as is intended to be explained with the following example of a contactor and with reference to the voltage ranges of the contactor shown in FIG. 1. At a rated voltage range 100 of from 24 volts to 240 volts (AC or DC voltage), according to the standards the contactor must be switched on in a voltage range 120 of from 85% of 24 volts, i.e. 20.4 volts, to 110% of 240 volts, i.e. 264 volts. According to the standard, the contactor may be released at 75% of 24 volts, i.e. at 18 volts, but must have been released at 20% of 240 volts, i.e. at 48 volts, for AC voltage (voltage range 140).
As can be seen in FIG. 1, the switch-on and switch-off ranges of the contactor overlap in the voltage range 160 of from 20.4 volts to 48 volts, in which range the contactor cannot be switched on.
In order for the limit values specified by the above standards to be observed and for the above-mentioned voltage range overlaps to be avoided, the voltage range of a switching device specified by a rated control supply-voltage must be selected to be relatively small, and manufacturers must provide a rather extensive range of switching devices that are suitable and designed for various rated voltage ranges.